This change implements a flood fill algorithm for the Bitmap class. This
will be leveraged by various Tools in PixelPaint. Moving the code into
Bitmap reduces the duplication of the algorithm throughout the
PixelPaint Tools (currently Bucket Tool and Wand Select).
The flood fill function requires you to pass in a threshold value (0 -
100) as well as a lambda for what to do when a pixel gets reached. The
lambda is provided an IntPoint representing the coordinates of the pixel
that was just reached.
The genericized lambda approach allows for a variety of things to be
done as the flood algorithm progresses. For example, the Bucket Tool
will paint each pixel that gets reached with the fill_color. The Wand
Select tool wont actually alter the bitmap itself, instead it uses the
reached pixels to alter a selection mask.
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